Question

Oxidized off-flavours in ghee are caused mainly due to __________.
(A) Aldehydes
(B) Ketones
(C) Hydro peroxides
(D) Free fatty acids

• (C) and (D) only.
• (B) and (C) only.
• (A) and (B) only.
• (A) and (D) only.

Hint:

Remember: Hydroperoxides are odorless primary oxidation intermediates.
The actual off-flavors of oxidative rancidity are caused by their volatile breakdown products: aldehydes and ketones.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Oxidative rancidity (lipid autoxidation) in fat-rich dairy products like ghee involves a series of free radical reactions affecting unsaturated fatty acids.
Although the reaction begins with the formation of primary oxidation products, the characteristic off-flavors are caused by volatile secondary products.

Step 2: Detailed Explanation:
Let us examine the role of each compound in the development of oxidized flavors:
1. Hydroperoxides (C): These are the primary products of lipid autoxidation.
Hydroperoxides are highly unstable, odorless, and tasteless.
They do not directly produce the sensory defects associated with oxidized flavors.
2. Aldehydes (A) and Ketones (B): As autoxidation progresses, the unstable hydroperoxides decompose via homolytic cleavage to yield a variety of volatile secondary products, primarily aliphatic aldehydes (such as hexanal, octenal, and nonenal) and ketones (such as unsaturated ketones).
These carbonyl compounds have extremely low flavor and odor thresholds (often in the parts-per-billion or parts-per-trillion range) and directly impart the characteristic metallic, cardboard-like, painty, and tallowy off-flavors associated with oxidized ghee.
3. Free fatty acids (D): These are products of lipid hydrolysis (hydrolytic rancidity), not autoxidation, and produce a soapy or pungent, sweaty off-flavor.

Step 3: Final Answer:
Oxidized off-flavors in ghee are primarily caused by aldehydes and ketones, which corresponds to (A) and (B) only.